


The Three of Us

by Demial



Category: Fate/Grand Order
Genre: Aftercare, Casual Sex, Cowgirl Position, F/M, Light Dom/sub, M/M, Multi, Oral Sex, Pegging, Spitroasting, Threesome - F/M/M, Vaginal Sex, a lil'
Language: English
Status: Completed
Published: 2019-04-08
Updated: 2019-04-08
Packaged: 2020-01-06 17:16:39
Rating: Explicit
Warnings: No Archive Warnings Apply
Chapters: 1
Words: 1,639
Publisher: archiveofourown.org
Story URL: https://archiveofourown.org/works/18392825
Author URL: https://archiveofourown.org/users/Demial/pseuds/Demial
Summary: Female reader. Based on Saber Diarmuid's line ingame about being excited to fight alongside Cu Chulainn. They both jump at the chance for a threesome after Diarmuid finds he's sexually attracted to Cu. You have a previous casual relationship with Diarmuid and Cu is added to the mix.





	The Three of Us

**Author's Note:**

> saber diarmuid is such a thicc, cute boy <3

"You summoned the Child of Light?!" Diarmuid asked. "I wish to fight alongside him. It would be the greatest honour."  
  
You were happy to hear that. Saber Diarmuid and Lancer Cu Chulainn would make a good team. With the many different personalities of your servants, all strong, it was difficult to put together teams that functioned. Along with a caster, you put the two Irishmen together right away and sent them off to fight as a supplement to your main team.  
  
So they went. Things were going well, you assumed, until Diarmuid came to speak to you. Before bedtime, the only time you had to talk. He wore a most serious expression and he sat you both down on your bed.  
  
"I have a confession."  
  
You nodded. "Okay." You couldn't imagine what could be wrong. Almost everyone likes him. He diligently maintained his weapons and he enjoyed training with his fellow servants. He was always fighting fit. Almost never returned to Chaldea with more than a scratch. "Go on," you encouraged.  
  
"Remember when I told you I admired Cu Chulainn?"  
  
"Yeah. Something happened? Did you fight?"  
  
He smiled slightly.  
  
"Yes, we did. In a good way." So they sparred. Alright. "But things got heated between us..."  
  
"You just told me that you didn't argue!"  
  
"No, heated in a...sexual way."  
  
"WHAT?"  
  
You had Diarmuid tell you all about it. At first, you were jealous. But the more he told you, the more aroused you became, picturing in detail what he described.  
  
You and Diarmuid had been intimate a few times before, almost immediately after he was summoned. While it was obvious that he was a pretty and capable man, you were smitten when you found he was a sweet and mild man also off the battlefield. He took well to being bossed around, your satisfaction being foremost in his mind. He made passionate love to you but neither of you had talked about about a relationship. Diarmuid giving another man a blowjob wasn't necessarily cheating. Especially with someone as attractive as Cu Chulainn, you concluded.  
  
"Ohhhh," you said when Diarmuid finished talking. You were gazing off somewhere else, the wheels already turning inside your head.  
  
Suddenly, you patted his arm.  
  
"I had an idea."  
  
You couldn't help the grin that spread across your face. It surprised him. He had expected your disapproval.  
  
"Master?"  
  
"What if...the three of us...?"  
  
His eyebrows met in the middle. He didn't get it.  
  
"What if you did that again but I was there?" you said.  
  
He thought you only wanted to watch. When you explained that you wanted to participate, he almost hit the ceiling with joy. His face beamed softly. He took your idea as a sign of your approval of what he had done with Cu. He returned your arm to your lap and stood up.  
  
"I'll go inform him-"  
  
"Nah. Let me do it."  
  
You had to go feel Cu Chulainn out first to see if he would accept you as the one in charge if he consented to the threesome.  
  
You mirrored the wicked grin you received from Cu upon hearing your plan. You wanted both of you to dominate Diarmuid, to have him in the centre. Cu couldn't agree fast enough.  
  
The next night, Cu sat on your bed. He had stripped off all his clothes, giving Diarmuid a pat on the butt in greeting. You, meanwhile, got yourself ready by slipping into a harness with a strapon that Diarmuid could handle comfortably.  
  
"Clothes off," you ordered Diarmuid. "Then do as Cu says."  
  
It was one thing to imagine the saber sucking off Cu, but it was another to actually watch it. Diarmuid worshipped Cu's cock with his lips and tongue like he had done to your labia in the past. He was such a good boy. And a good boy deserves a good pegging.  
  
Getting the dildo inserted, you worked on Diarmuid from behind, holding your lovely boy by his hips.  
  
Cu fell back onto the bed, letting out a pleased groan.  
  
"That feels good," he said.  
  
You rolled your hips gently at Diarmuid's ass, content to just give him pleasure. Not fucking him too fast or hard. His wide, well-muscled back was a relaxing view. You sank your teeth into the thick flesh a few times before this was over.  
  
After a while, Cu sat up.  
  
"Heh. I think I lost him."  
  
Cu's cock had slipped out of Diarmuid's mouth. It was still open, husky little moans puffing out. Cu grinned hungrily and gripped the saber's jaw, watching closely.  
  
"Okay, I'll go easier on him," you said.  
  
"...no," Diarmuid protested.  
  
"Yes!" You smacked one of his ass cheeks. "You gotta be a good boy and service Cu."  
  
Your hips lazed forward and back, concentrating most on a consistent speed. Diarmuid whined with the effort of shoving his own pleasure to the side and nuzzled Cu's cock, which hung in front of his face. He took Cu into his mouth, deep as he could, as much length as he could. He glanced up at Cu's lazy grin, watching the lancer like a baby watches its mother during breastfeeding.  
  
"Good saber," Cu rumbled quietly.  
  
You grinned. "He really is."  
  
Diarmuid moaned, his eyelids dipping low.  
  
"Oh? What's that?" Cu asked, perking up.  
  
"This good boy has a praise kink."  
  
"Ahhhh..."  
  
Cu took that information and ran. He took Diarmuid's face in both hands. Cu let the compliments flow. It was easy, praising the saber's looks. Praising his honour and the way he stood for it. Diarmuid's body was a perfect subject. You helped out by groping the specific body part mentioned by Cu. Cupping his firm ass, tugging at his little brown nipples, and teasing his inner thighs with caresses. His cock jumped constantly, as Diarmuid barreled towards orgasm. You hadn't even touched his cock yet.  
  
Diarmuid lost control of his mouth again. Cu kept holding his face. With your permission, he began to rock his hips into Diarmuid's open mouth.  
  
"Fuck. You look so pretty," moaned Cu.  
  
He made a mess of Diarmuid's mouth. Saliva leaked out of the corners. Cu pulled out and slapped Diarmuid's cheek a few times with his cock, smearing wetness there. The saber blushed deeply, enjoying the attention more than he expected. He whined and mouthed at Cu's cock, wanting it back inside, on his tongue.  
  
Cu cocked his head. "He wants it."  
  
"Give to him," you said. "He earned it."  
  
"Heh." He grinned. "Yes, Ma'am."  
  
Cu buried his fingers into Diarmuid's unruly hair this time and gripped the locks. He guided his cock easily into the saber's mouth. Cu thrusted with a purpose, getting off on the seal provided by the other's weak mouth. Diarmuid's gaze went through the lancer, letting himself be used on both ends.  
  
"Fffuck. Fuck....fuck..."  
  
Cu pulled back until he was just inside the warmth of Diarmuid's mouth and released his cum. Diarmuid swallowed eagerly, his adam's apple bobbing a few times.  
  
Cu recovered quickly. He took a hold of Diarmuid's jaw again. Cu planted a quick kiss on the saber's forehead. It seemed appropriate, with the way Diarmuid was gazing up at him in hazy admiration.  
  
"You did good," Cu said.  
  
You gave your Diarmuid a pat on the side of his hip and pulled out. He was gone enough for you to throw him to the floor on his back.  
  
"You're going to finish inside me," you told him, leaving no room for disagreement.  
  
You stood up and pulled off the strapon, letting it fall to the floor with rubbery thud. You went to stand over Diarmuid's lap. He put his hand to your ankle with an admiring smile.  
  
You were about to say something but decided you wanted him inside you _right now_ instead.  
  
"Lube, lube," you told Cu, beckoning impatiently.  
  
He tossed it to you, settling onto the floor to watch.  
  
You poured a puddle of lube into your hand. Reached down. Smeared it all over yourself. Then up and down Diarmuid's length.  
  
His hand gripped your ankle and he gritted his teeth.  
  
"Don't cum yet," you said.  
  
And down you sat, forcing his cock into your cunt. You held him steady, wiggling around on his cockhead and working it deeper. You would rather have him inside now and hurt than wait and risk him cumming. Your butt finally met his thighs and you beckoned Cu over.  
  
"Eh?" he questioned.  
  
He came to stand next to you. You raised your arms.  
  
"Let me hold onto you."  
  
"Ahhh." Cu understood right away, grabbing your hands and holding them there.  
  
You used Cu to get yourself up and then let yourself back down. You bounced on Diarmuid's cock with Cu's help, panting.  
  
Diarmuid himself, lay tensed below you, his face scrunched up. You knew he was on the edge when his mouth opened far.  
  
"M-master?!" he cried, his thighs shaking.  
  
An amused sigh interrupted your puffing.  
  
"You never need my permission, Sweet Baby. You can cum."  
  
As soon his cock expanded your walls to pump his seed into you, your ass hit his lap. You growled low and your lip slid through your teeth as he filled you up. Your favourite part of fucking him. He gladly endured your own orgasm after, with your cunt contracting around his oversensitive cock.  
  
Cu was all content purrs and quiet growls after that. He helped you get Diarmuid into your bed. Normally, you wanted more space to yourself when you slept. Tonight, you were so sleepy and content that you welcomed even Cu under the covers. Diarmuid had already succumbed to the steady breathing of sleep. Cu's presence squished you against his back. Cu settled in, yawned, and rolled over to sleep, himself. You were worrying that you might not get there, too, when you fell unconscious.


End file.
